1. Field of the Invention
The present invention relates generally to a genetic sequence encoding a polypeptide having flavonoid 3′,5′-hydroxylase (F3′5′H) activity and to the use of the genetic sequence and/or its corresponding polypeptide thereof inter alia to manipulate color in flowers or parts thereof or in other plant tissue. More particularly, the F3′5′H has the ability to modulate dihydrokaempferol (DHK) metabolism as well as the metabolism of other substrates such as dihydroquercetin (DHQ), naringenin and eriodictyol. Even more particularly, the present invention provides a genetic sequence encoding a polypeptide having F3′5′H activity when expressed in rose or gerbera or botanically related plants. The instant invention further relates to antisense and sense molecules or RNAi-inducing molecules corresponding to all or part of the subject genetic sequence or a transcript thereof as well as to genetically modified plants as well as cut flowers, parts and reproductive tissue from such plants. The present invention further relates to promoters which operate efficiently in plants such as rose, gerbera or botanically related plants.
2. Description of Prior Art
Reference to any prior art in this specification is not, and should not be taken as an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.
Bibliographic details of references provided in the subject specification are listed at the end of the specification.
The flower or ornamental plant industry strives to develop new and different varieties of flowers and/or plants. An effective way to create such novel varieties is through the manipulation of flower color. Classical breeding techniques have been used with some success to produce a wide range of colors for almost all of the commercial varieties of flowers and/or plants available today. This approach has been limited, however, by the constraints of a particular species' gene pool and for this reason it is rare for a single species to have the full spectrum of colored varieties. For example, the development of novel colored varieties of plants or plant parts such as flowers, foliage and stems would offer a significant opportunity in both the cut flower and ornamental markets. In the flower or ornamental plant industry, the development of novel colored varieties of major flowering species such as rose, chrysanthemum, tulip, lily, carnation, gerbera, orchid, lisianthus, begonia, torenia, geranium, petunia, nierembergia, pelargonium, iris, impatiens and cyclamen would be of great interest. A more specific example would be the development of a blue rose or gerbera for the cut flower market.
In addition, the development of novel colored varieties of plant parts such as vegetables, fruits and seeds would offer significant opportunities in agriculture. For example, novel colored seeds would be useful as proprietary tags for plants. Furthermore modifications to flavonoids common to berries or fruits including grapes and apples and their juices including wine have the potential to impart altered style characteristics of value to such fruit and byproduct industries.
Flower color is predominantly due to three types of pigment: flavonoids, carotenoids and betalains. Of the three, the flavonoids are the most common and contribute a range of colors from yellow to red to blue. The flavonoid molecules that make the major contribution to flower color are the anthocyanins, which are glycosylated derivatives of cyanidin and its methylated derivative peonidin, delphinidin or delphinidin-based molecules and its methylated derivatives petunidin and malvidin and pelargonidin. Anthocyanins are localised in the vacuole of the epidermal cells of petals or the vacuole of the sub epidermal cells of leaves.
The flavonoid pigments are secondary metabolites of the phenylpropanoid pathway. The biosynthetic pathway for the flavonoid pigments (flavonoid pathway) is well established, (Holton and Cornish, Plant Cell 7: 1071-1083, 1993; Mol et al., Trends Plant Sci. 3: 212-217, 1998; Winkel-Shirley, Plant Physiol. 126: 485-493, 2001a; and Winkel-Shirley, Plant Physiol. 127: 1399-1404, 2001b) and is shown in FIGS. 1A and B. Three reactions and enzymes are involved in the conversion of phenylalanine to p-coumaroyl-CoA, one of the first key substrates in the flavonoid pathway. The enzymes are phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H) and 4-coumarate: CoA ligase (4CL). The first committed step in the pathway involves the condensation of three molecules of malonyl-CoA (provided by the action of acetyl CoA carboxylase (ACC) on acetyl CoA and CO2) with one molecule of p-coumaroyl-CoA. This reaction is catalysed by the enzyme chalcone synthase (CHS). The product of this reaction, 2′4,4′,6′, tetrahydroxy-chalcone, is normally rapidly isomerized by the enzyme chalcone flavanone isomerase (CHI) to produce naringenin. Naringenin is subsequently hydroxylated at the 3 position of the central ring by flavanone 3-hydroxylase (F3H) to produce dihydrokaempferol (DHK).
The pattern of hydroxylation of the B-ring of dihydrokaempferol (DHK) plays a key role in determining petal color. The B-ring can be hydroxylated at either the 3′, or both the 3′ and 5′ positions, to produce dihydroquercetin (DHQ) or dihydromyricetin (DHM), respectively. Two key enzymes involved in this part of the pathway are flavonoid 3′-hydroxylase and flavonoid 3′,5′-hydroxylase, both of the cytochrome P450 class of enzymes. Cytochrome P450 enzymes are widespread in nature and genes have been isolated and sequenced from vertebrates, insects, yeasts, fungi, bacteria and plants.
Flavonoid 3′-hydroxylase (F3′H) is a key enzyme in the flavonoid pathway leading to the cyanidin-based pigments which, in many plant species (for example Rosa spp., Dianthus spp., Petunia spp., begonia, cyclamen, impatiens, morning glory and chrysanthemum), contribute to red and pink flower color.
Flavonoid 3′,5′-hydroxylase (F3′5′H) is a key enzyme in the flavonoid pathway leading to the delphinidin-based pigments which, in many plant species (for example, Petunia spp., Viola spp., Lisianthus spp., Gentiana spp., Sollya spp., Salvia spp., Clitoria spp., Kennedia spp., Campanula spp., Lavandula spp., Verbena spp., Torenia spp., Delphinium spp., Solanum spp., Cineraria spp., Vitis spp., Babiana stricra, Pinus spp., Picea spp., Larix spp., Phaseolus spp., Vaccinium spp., Cyclamen spp., Iris spp., Pelargonium sp., Liparleae, Geranium spp., Pisum spp., Lathyrus spp., Catharanthus spp., Malvia spp., Mucuna spp., Vida spp., Sainipaulia spp., Lagerstroemia spp., bouchina spp., Plumbago spp., Hypocalyptus spp., Rhododendron spp., Linum spp., Macroptilium spp., Hibiscus spp., Hydrangea spp., Cymbidium spp., Millettia spp., Hedysarum spp., Lespedeza spp., Asparagus spp. Antigonon spp., Pisum spp., Freesia spp., Brunella spp., Clarkia spp., etc.), contribute to purple and blue flower color. Many plant species such as roses, gerberas, chrysanthemums and carnations, do not produce delphinidin-based pigments because they lack a F3′5′H activity.
The next step in the pathway, leading to the production of the colored anthocyanins from the dihydroflavonols (DBK, DHQ, DHM), involves dihydroflavonol-4-reductase (DFR) leading to the production of the leucoanthocyanidins. The leucoanthocyanidins are subsequently converted to the anthocyanidins, pelargonidin, cyanidin and delphinidin or delphinidin-based molecules. These flavonoid molecules are unstable under normal physiological conditions and glycosylation at the 3-position, through the action of glycosyltransferases, stabilizes the anthocyanidin molecule thus allowing accumulation of the anthocyanins. In general, the glycosyltransferases transfer the sugar moieties from UDP sugars to the flavonoid molecules and show high specificities for the position of glycosylation and relatively low specificities for the acceptor substrates (Seitz and Hinderer, Anthocyanins. In: Cell Culture and Somatic Cell Genetics of Plants. Constabel, F. and Vasil, I. K. (eds.), Academic Press, New York, USA, 5: 49-76, 1988). Anthocyanins can occur as 3-monosides, 3-biosides and 3-triosides as well as 3,5-diglycosides and 3,7-diglycosides associated with the sugars glucose, galactose, rhamnose, arabinose and xylose (Strack and Wray, In: The Flavonoids—Advances in Research since 1986. Harborne, J. B. (ed), Chapman and Hall, London, UK, 1-22, 1993).
Glycosyltransferases involved in the stabilisation of the anthocyanidin molecule include UDP glucose: flavonoid 3-glucosyltransferase (3GT), which transfers a glucose moiety from UDP glucose to the 3-O-position of the anthocyanidin molecule to produce anthocyanidin 3-O-glucoside.
In petunia and pansy (amongst others), anthocyanidin 3-O-glucoside are generally glycosylated by another glycosyltransferase, UDP rhamnose: anthocyanidin 3-glucoside rhamnosyltransferase (3RT), which adds a rhamnose group to the 3-O-bound glucose of the anthocyanin molecule to produce the anthocyanidin 3-rutinosides, and once acylated, can be further modified by UDP: glucose anthocyanin 5 glucosyltransferase (5GT). However, in roses (amongst others), the anthocyanidin 3-O-glucosides are generally glycosylated by another glycosyltransferase, UDP: glucose anthocyanin 5 glucosyltransferase (5GT) to produce anthocyanidin 3,5 diglucosides.
Many anthocyanidin glycosides exist in the form of acylated derivatives. The acyl groups that modify the anthocyanidin glycosides can be divided into two major classes based upon their structure. The aliphatic acyl groups include malonic acid or succinic acid and the aromatic class include the hydroxy cinnamic acids such as p-coumaric acid, caffeic acid and ferulic acid and the benzoic acids such as p-hydroxybenzoic acid.
Methylation at the 3′ and 5′ positions of the B-ring of anthocyanidin glycosides can also occur. Methylation of cyanidin-based pigments leads to the production of peonidin. Methylation of the 3′ position of delphinidin-based pigments results in the production of petunidin, whilst methylation of the 3′ and 5′ positions results in malvidin production. Methylation of malvidin can also occur at the 5-O and 7-O positions to produce capensinin (5-O-methyl malvidin) and 5,7-di-O-methyl malvidin.
In addition to the above modifications, pH of the vacuole or compartment where pigments are localised and copigmentation with other flavonoids such as flavonols and flavones can affect petal color. Flavonols and flavones can also be aromatically acylated (Brouillard and Dangles, In: The Flavonoids—Advances in Research since 1986. Harborne, J. B. (ed), Chapman and Hall, London, UK, 1-22, 1993).
The ability to control F3′5′H activity, or other enzymes involved in the flavonoid pathway, in flowering plants would provide a means of manipulating the color of plant parts such as petals, fruit, leaves, sepals, seeds etc. Different colored versions of a single cultivar could thereby be generated and in some instances a single species would be able to produce a broader spectrum of colors.
Two nucleotide sequences (referred to herein as SEQ ID NO:1 and SEQ ID NO:3) encoding petunia F3′5′Hs have been cloned (see international Patent Application No. PCT/AU92/00334 and Holton et al., Nature, 366: 276-279, 1993a). These sequences were efficient in modulating 3′,5′ hydroxylation of flavonoids in petunia (see International Patent Application No. PCT/AU92/00334 incorporated herein by reference and Holton et al., 1993a, supra), tobacco (see International Patent Application No. PCT/AU92/00334 incorporated herein by reference) and carnations (see International Patent Application No. PCT/AU96/00296 incorporated herein by reference). Surprisingly, however, inclusion of these sequences in standard expression cassettes, did not lead to the production of intact or full-length transcripts as detectable by RNA or Northern blot analysis and consequently 3′,5′-hydroxylated flavonoids were not produced in roses. There is a need, therefore, to identify further genetic sequences encoding F3′5′Hs which efficiently accumulate and are then able to modulate 3′,5′ hydroxylation of flavonoids such as anthocyanins in roses and other key commercial plant species.